Fabric filters, sometimes called bag-houses, are often used for separating dust particles from a dust-laden gas, such as a flue gas of a coal-fired boiler, a waste incinerator plant, an electric arc furnace or another process in which a dust-laden gas is generated. U.S. Pat. No. 4,336,035 and EP 168 369 A2 describe typical fabric filters in which a dust-laden gas is passed into a housing. Inside the housing a number of textile filter bags are located. Each bag is supported by a wire cage such that a gas may pass through the textile material and into the bag leaving the dust on the outside of the bag. During operation the dust forms a cake on the outside of the bag. By intermittent high pressure pulsing the bag is forced to expand rapidly thereby removing the cake of dust from the bag. The dust is collected at the bottom of the housing.
U.S. Pat. No. 5,505,766 to Chang describes a bag-house having three parallel compartments. It is often desired to shut off one compartment in order to be able to inspect the bags of that compartment while the other compartments remain in operation. This would, however, require one shut off valve for the dust transport line of each compartment. Such a system is quite expensive both in investment and maintenance cost.